Return salmon path for users, basic incoming salmon handling.

lib/pleroma/web/activity_pub/activity_pub.ex

lib/pleroma/web/ostatus/feed_representer.ex

lib/pleroma/web/ostatus/ostatus.ex

lib/pleroma/web/ostatus/ostatus_controller.ex

lib/pleroma/web/router.ex

lib/pleroma/web/twitter_api/twitter_api.ex

lib/pleroma/web/web_finger/web_finger.ex

test/web/ostatus/feed_representer_test.exs

test/web/ostatus/ostatus_test.exs